Pressure transmitters are used to remotely monitor the pressure of a process fluid. Remote seals, or remote diaphragm assemblies, are often used to space the pressure transmitter from hazardous measurement environments, or for linking the pressure transmitter with inconveniently located process fluid. For example, remote seals are often used with corrosive or high temperature process fluids. In those situations, a remote seal having a diaphragm assembly and a capillary tube can be used to connect the pressure transmitter to the process fluid while the pressure transmitter is located a safe distance away. The capillary tube may extend tens of meters in order to couple the pressure transmitter with the process fluid. The remote seal communicates hydraulically with the process fluid through a thin flexible diaphragm, which is used to isolate the process fluid from a fill fluid used in the capillary tube. As the diaphragm flexes, the incompressible fill fluid translates the pressure change through the capillary tube to a diaphragm of a pressure sensor located in the pressure transmitter. Deflection of the pressure transmitter diaphragm is transmitted through a similar method to a pressure sensor disposed within the transmitter, which produces a signal related to the pressure of the process fluid.
Remote seal hydraulic systems are typically filled with the substantially incompressible fluid at the factory with a precise amount of fill fluid and then sealed. System performance is correlated with the precise level of fill fluid and is degraded with any oil leakage or the presence of air in the fill fluid. For severe applications, such as high temperature or high process vacuum service, specialized factory production methods are used to remove air from the fill fluid and permanently seal the hydraulic system. For some less severe applications, loss of a minute amount of fill fluid is acceptable.
One recent advance in the art of remote process seal couplings is provided in U.S. Pat. No. 7,258,017 and is entitled Industrial Process Pressure Transmitter with Field Repairable Remote Seals. This patent describes the ability to service a remote seal in the field, by decoupling and recoupling a remote process seal to a process pressure transmitter. While the quick-connect seals of the '017 patent are highly useful and provide important advantages in the field, in fact there are some instances where such couplings may not fully meet all of the application's requirements. For example, remote seals are often separated from the process fluid pressure transmitters through a barrier or containment structure, such as in the context of nuclear process measurements and control. Such applications may set forth a maximum dimension for penetrations through containment structures to assure that the process is contained. Narrow penetrations within the containment structure may inhibit the ability to route the remote seals to the installation location. For example, one specific containment application permits penetrations no larger than 19 mm in diameter, which generally prohibits the routing of a remote seal assembly through the penetration.